The present invention relates to air bag restraint systems for motor vehicles and in particular to air bag restraint systems in which an air bag module with mechanical trigger is located in the boss of the steering wheel of the vehicle.
It is proposed to mount an air bag module of a restraint system for a motor vehicle in the boss of the vehicle's steering wheel, so that in a collision, the air bag will be deployed in front of the driver to prevent the driver coming into contact with the steering wheel or windscreen. The air bag module comprises an inflator which includes a pyrotechnic device, a trigger mechanism which in a collision will initiate a fast burn process to rapidly produce large volumes of gases which will inflate the air bag. For safety reasons, the inflator has a spring loaded plunger which must first be depressed to arm the inflator before it can be triggered. This is achieved by an arming screw, which engages an inclined face on the plunger, so that as the arming screw is tightened, the plunger will be depressed.
For maintenance purposes, it is occasionally necessary to remove the air bag module and/or steering wheel. When doing so, the inflator should be first disarmed by unscrewing the arming screw. The present invention provides an interlock mechanism to ensure that the inflator is disarmed before removal of the air bag module and/or steering wheel and re-armed when the steering wheel and/or air bag module are re-fitted.